Generating and characterizing the perfect elimination orderings of a chordal graph

We develop a constant time transposition "oracle" for the set of perfect elimination orderings of chordal graphs. Using this oracle, we can generate a Gray code of all perfect elimination orderings in constant amortized time using known results about antimatroids. Using clique trees, we show how the initialization of the algorithm can be performed in linear time. We also develop two new characterizations of perfect elimination orderings: one in terms of chordless path; and the other in terms of minimal u-v separators